Evaluation of timber floor systems for fire resistance and other performance requirements

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University of Canterbury

Degree Level

Doctoral

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Timber is a traditional building material used for floor construction in historic buildings and
is widely used today in domestic and residential construction. There is increased interest in
timber for long span floor systems in commercial and multi-storey residential applications. A
major reason for this interest is timbers high strength-to-weight ratio, and when used in
floors, can lead to significantly lighter buildings. These resulting weight savings allow for
smaller foundations and less lateral load applied to seismic-resisting structural systems.
New timber and timber-concrete composite floor systems have emerged to provide increased
span lengths. These longer span timber floors are typically achieved with deep solid timber
joists of laminated veneer lumber or glulam, solid timber laminated deck plates and timberconcrete
composite floor systems. There are several engineered timber floor joist and timber
floor truss products already available in Australasia. New floor systems recently introduced
into the market include Potius stressed-skin floors and Flexus floor, both of which are
prefabricated into floor panels off site.
The timber-concrete composite floor system utilises the compressive strength of concrete and
the tensile strength of timber. The composite concrete topping adds weight to the floor
system, however this is offset by structural, fire and acoustic benefits. Currently there is
ongoing study of timber-concrete composite floor systems at the University of Canterbury in
Christchurch, and stressed-skin floor systems at the University of Technology in Sydney, so
that these longer span floor systems can be used for building design in the near future.
Gypsum board ceilings are typically installed beneath timber floor systems to provide an
enclosed space for distribution of building services behind a visibly uniform finish. A
gypsum board ceiling can also provide fire resistance and acoustic performance and the
information for these aspects is readily available. Alternatively, some floor systems allow
exposed timber joists or timber surfaces. In these situations, fire resistance and acoustic
performance are specifically designed.